This invention relates to an apparatus and method for transferring and displaying a superimposed image using a three-dimensional computer graphics (3DCG) image in a picture upon transferring information for rapid display such as a sport broadcasting, an election advisory, or the like.
A basic principle of rendering a 3DCG image in real time and superimposing the mixed signal on an input television (TV) signal will be described below by referring to the drawing for convenience of explanation. FIG. 1 is a schematic diagram illustrating a process for superimposing a 3DCG image on an input TV signal in real time. As shown in FIG. 1, information required for rendering a 3DCG image is pre-calculated to be sent to a three-dimensional graphics accelerator (A), and then a 3DCG image is formed by rendering the pre-calculated information in the accelerator (B). The formed 3DCG image is transferred to a superimposer and is pre-mixed prior to composing it with an input TV signal (C). A mixing process (D) forms a broadcasting image including the TV signal mixed with superimposed images and a broadcasting image signal is transmitted (E).
In order to realize a visually smooth animation, it is necessary to display a 3DCG image to meet National Television System Committee (NTSC) broadcasting system or Phase Alteration by Line (PAL) broadcasting system (for example, about 60 fields per second in the NTSC broadcasting system). However, in order to render a 3DCG image and then to mix the image with the input TV signal and broadcast the mixed signal in real time processing, a period of time T required for serial processing from the pre-calculating process (A) to the mixing and transferring process (D) is limited to about 16.67 msec (60 field/second) to 20 msec (50 field/second). In addition, since a given period of time is required to transfer the 3DCG image datum from the accelerator to a system memory and from the system memory to the superimposer, respectively, a period of time for rendering process must be necessarily shorten. Consequently, when a complex 3DCG image is transferred as a superimposed image, all processes cannot be completed within the above time limit of period and thus it is difficult to transfer necessary fields.
Thus, a special system that is designed for the purpose of a broadcasting application to process a 3DCG image was used. The special system has a special hardware including a function of superimposing and a function of processing the 3DCG image. The system having these functions takes a high cost in production due to high specialty. It is difficult for broadcasting staffs using the system to adopt many systems on the aspect of cost performance ratio. On the other hand, a performance of a current three-dimensional graphics accelerator is progressing and current 3D accelerators will soon become obsolete or outmoded. Accordingly, since a new, specialized system would clearly be obsolete soon after it was bought, it was a mistake to introduce a new expensive three-dimensional graphics accelerator integrated with a transferring function and a hardware that are designed for the above purpose of broadcasting.
As a measure for replacing such a very expensive special broadcasting system and for shortening a process period of time to transfer a 3DCG image, Japanese Patent Public Disclosure No. HEISEI 5 (1993)-91413 discloses a superimposing apparatus in which, before broadcasting, a 3DCG image that rendered a necessary image has been once stored in a storage device such as a hard disk memory or the like, and then the stored 3DCG image is invoked at a suitable timing upon broadcasting the 3DCG image and is mixed and transferred.
However, such a superimposing apparatus requires a mass-storage device since the apparatus must pre-render necessary images and store them in the storage device. Since the apparatus also requires a pre-rendering time, it induces vainness in economy and time. Accordingly, the apparatus cannot comply with an application of a superimposer requiring immediacy.